1. Field of the Invention
The present invention relates to crossed-field amplifiers, and more precisely, to a crossed-field amplifier using internally cooled forward wave anode vanes.
2. Description of the Related Art
Crossed-field amplifiers (CFAs) have been used for several years in electronic systems that require high RF power, such as radar systems. A CFA operates by passing an RF signal through a high voltage electric field formed between a cathode and an anode. The cathode emits electrons which interact with an RF wave as it travels through a slow-wave path provided in the anode structure surrounding the cathode. The RF wave is guided by a magnetic field, which crosses the electric field perpendicularly.
Traditionally, the cathode in such an amplifier is based on a thermionic-type emitter that operates on a principle of direct heating to boil off electrons. Non-thermionic emitter cathodes are also available. These cathodes are formed from pure metal, such as molybdenum, platinum or nickel, which emits secondary electrons due to bombardment of the metal with primary electrons. Since there is no cathode heating, the non-thermionic emitter cathodes have improved life capability over thermionic emitter cathodes.
The anode structure comprises a plurality of vanes disposed coaxially around the cathode. When electrons leave the cathode of the CFA in a direction perpendicular to the magnetic field, the field causes a force to act at right angles to the electron motion. The electrons then spiral into orbit around the cathode instead of moving with the electric field. Most of the electrons gradually move toward the anode, giving up potential energy to the RF wave as they interact with the anode slow-wave structure.
However, a problem with crossed-field amplifiers is their relatively short life span, especially when operated at high average power. To impart the energy into the RF wave, there must be high electron discharge into the anode structure that generates heat build-up. At high power levels, the electron discharge can damage the anode vanes and the protective molybdenum coating on the vane tips can burn off.
To rectify the problem, liquid cooling systems have been used in conventional crossed-field amplifiers. An example of a liquid cooled crossed-field amplifier is disclosed in U.S. Pat. No. 4,700,109, issued Oct. 13, 1987 to G. R. MacPhail. Usually, oil or water coolant was supplied to the backwall of the anode vanes. But this standard backwall cooled anode design was sometimes inadequate to meet system requirements, since the vane tips are not close enough to the back wall to obtain the beneficial effects of the liquid coolant.
Accordingly, a need presently exists for improved cooling of each vane of a standard double helix coupled vane crossed-field amplifier.